Evaluation of a method for sensing the oil level and oil quality using a capacitive level sensor

Abstract

In this undergraduate thesis, a system to measure the oil level and quality with a capacitive sensor, applying the Impedance Spectroscopy technique is proposed. The project was developed during the author’s internship in the company ZF Friedrichshafen AG, located in Friedrichshafen, Germany, which lasted three and a half months. First, a study concerning the application of the Impedance Spectroscopy method to various applications, its efficiency and characteristics, as well as for the measurement of oil impedance, based in other works were made. After, for the evaluation of the system, some tests were taken, in order to analyze the feasibility and practicability of it. For these experiments, it was considered four distinct variables, which could change the oil impedance, leading to different measurements. These four variables were: level, temperature, age and water percentage. As results, the level measurement demonstrated a good linear relation between the level applied to the sensor and the impedance measured. The temperature showed a very small alteration in the impedance values. For different oil ages, the measurements showed almost no difference and just two age samples were tested, guiding to inconclusive results about the concerning the oil age differentiation. Considering the water contamination, with small amounts of water in the oil, the impedance presented a decay that could be detect in the measurements. And, related to the frequency range, it was found that the best spectrum for a better system performance, examining the impedance and phase measurements, was between 30 kHz and 70 kHz. Overall, the system, even presenting some limitations and errors, showed to be feasible for measurement of the oil level and quality and for the application in off-highway transmissions.